A radio frequency signal transmission device conventionally comprises a digital and/or analog circuit for generating radio frequency signals to be transmitted, a power analog circuit for amplifying the radio frequency signals, and an antenna coupled to the output of the power amplifier, generally via an impedance matching and/or harmonics filtering circuit.
The radio frequency signals transmitted by such a device may be frequency-modulated signals or phase-modulated signals, that is, alternative current (AC) signals of constant amplitude, the data to be transmitted being coded by variations of the signal frequency or phase.
As a variation, the transmitted radio frequency signals may be amplitude-modulated signals, that is, AC signals of constant frequency, the data to be transmitted being coded by amplitude variations of the signal.
In a device transmitting frequency-modulated signals or phase-modulated signals, the power amplifier may be a so-called class-E amplifier. This type of amplifier indeed has a good efficiency for the amplification of radio frequency signals of constant amplitude.
Class-E amplifiers however have no linear operating state, and are thus not adapted to the amplification of amplitude-modulated radio frequency signals.
In certain applications, it is desired to alternately transmit frequency-modulated radio frequency signals or phase-modulated radio frequency signals, or amplitude-modulated radio frequency signals.
To achieve this, a possible solution is to provide two different power amplifiers, one adapted to the amplification of the frequency-modulated signals or phase-modulated signals, and the other adapted to the amplification of the amplitude-modulated signals. This may however raise problems of cost, bulk, and/or electric power consumption.